Sound signal



R. M. CRITCHFIELD 1,994,574

SOUND SIGNAL Filed April 18, 1927 March 19, 1935.

' Irma/450a G 484 .1

f 'v'yem -3 Patented Mar. 19, 1935 7 PATENT orrics SOUND SIGNAL Robert M. 'C'i'itchfi'eld, Anderson, Ind, assignor,

by mesne assignments, to General Motors Corporation, Detroit, Mich.,,a corporation of Delaware Application April 13, 1927,Serial No. 184,507

11 Claims.

v obtaining only such movement of. the diaphragm as will be conducive to the production of the best tone.

' My copending application Serial No. 112,269 filed May 23, 1926, granted December 25, 1928 as Letters Patent No.'1,696,625, describes amagnetic circuit ofjsimilar character intended to. produce only natural'movement of-the diaphragmg -and. the present invention is an improvement thereon intended toaccomplish the desirable -results referred to by a simpler constructionj These and other objects are accomplished by providing an air gap between the armature and pole piece, which air gap isconstructed and ar-.

ranged to carry a part of the fluxirom'the pole piece to the core, and so as to be less sensitive to variation in manufacture and assembly of the contributing parts... In perfecting the improvement, an annular pole piece has been brought into cooperation and combination with aflanged,

. armature assembly, whereby two gaps areformed between the armature and pole piece, that include a cylindrical gap lying between the edges of the armature and the annular pole piece, and a fiat annular gap lying between the annular. po-le piece and an overhanging flange of the armature. Introduction of the cylindrical gap to carry a part of the flux from the annular pole piece to the core makes it possible to decrease the distance between the annular pole piece and the core without 'from the pole piece to the core. As aiurther result the area, the length, and the average diameter of the annular gap betweenthe annular pole piece andthe armature flange maybe substantially decreased without affecting the proper movement of the diaphragm to produce a good tone. Moreover, the magnetic circuit is made more effective to increase the blow of the armature upon the core. 7 i

Further objects and-advantages of the present invention will be apparent from the follow-- ing description, reference being had to the accompanying drawing, wherein a preferred form of embodiment of the present invention is clearly shown.

danger of the flux passing directly In the drawing: Fig. 1 is a rear view of the horn with the cover removed.

Fig. 2 is a section taken along Fig. 1. V

Fig. 3 is a detail view of a terminal plate. Fig. 4 is a detail View of the contact carrying terminal plate. i Fig. 5 isa detail view of insulator for the resilient contact arm which is of the same shape as this insulator; l i i Fig. 6 is a detail View of a terminal clip; and Fig. '7 is a fragmentary sectional view on line 77 of Fig. 2. i

Referring to the drawing, the numeral v designates the projector of the horn,,having a throatpo-rtion 21. provided with anoutwardly. extending, annular flange 22.- Adjacent the flange, the projector has an annular ridge 23,. thus providing an annular channel in ,which'. one edge of the dish-shaped projector. collar 24; is secured. An outwardly extending annular" flange 25 forms a seat upon which the diaphragm. 32 rests, said diaphragm being held in position by an annular edge 27 formed on the flange-25. The annular flange 28 of the motor base 29fflts within the edge 27 and engages the' diaphragm 32, which, like the flanges 25 and 28 is .apertured toreceive screws 30 cooperating with nuts,? 1 for clamping the edge of said diaphragm between the flanges 25 and 28. r

The diaphragm 32 is provided with an aperture 32a (see Fig. '7) which is a segment of a circle in shape. The aperture 32a receives a flanged nut 33 having a flat 33a on-its shank. The nut 33 cooperateswith the threaded shank 34 of "an armature which includes a head 35 having an annular flange 36. The shank' 34 extends through. a thin washer 37, the'diaphra'gm 32,

the line 2+2 a washers 38 and 39, a resonator disc 46, a lock 40.

washer 41 and threadedly through a nut 42. The shank 3 1 has a screw driver slot 34a. If the nut i2 is loosened the shank 34 may be turned to adjust the distance between the armature head 35 and the end of a magnet core 66.

The motor base 29 made of magnetic material is dished, providing two portions lying in different planes, relative to each other and to the flange 28 of the motor base. The outer portion is designated by the numeral 29a and the portion l'ying'in a plane between the outer portion and the flange 28 is designated by the numeral 29b An aperture 43 is provided in the portion-29c, a portion thereof being coaxial with the armature head 35 and of such size that said head,

Portion 29b of the motor-base is apertur'ed at" 44, being in fact an extension of the central aperture 43 as shown in Fig. 2. On the portion 29b is insulatingly mounted the circuit controller and its terminals. This circuit controller comprises the following elements arranged in superposed relation on the portion 29b; insulator 46, terminal plate 47 which supports the stationary contact 60, insulator lining plate 48 provided with, an aperture 48a at its free end, resilient blade 49 of the same shape as part 48 and carrying the contact 61 extending through theaperture 48a and engaging the stationary contact 60, wire receiving clip 50, insulator 51, terminal plate 52 provided with a wire receiving portion 52a and insulating ch'ver plate 53. All of these elements except plate 53 are apertured to receive insulating sleeves 54 which surround the rivets 55 which hold these parts in assembled relation. The resilient plate 49 and its insulating lining plate 48 extendinto the'path of movement of the armature so that the flange 36 will engage said insulating plate 48 to move the contact 61 out of engagement with the cooperating stationary 'contactwhen the armature is moved into its attracted position. Terminal plates 47 and 52 are each provided withwire attaching screws 62 at their outer ends the screw holes being shown at 62a in Figs."4 andj5. The

plate 47 is bent to extend into the aperture 44 so as to lie in the proper position for locatingthe.

contact in engagement with the contact 61 when the armature flange 36 is held in unattracted position; by the diaphragm 32.

The motor-base 29 supports a yoke 65 ofrmage netic material to which the core 66 is attached so that the free end of "the fcore .is substantially coaxial'with the armature shank and head. The core fifi is surround'edby an electromagnet wind ing 67 one wire receiving portion 52a of the terminal plate 52, thefother end 671) 'of which is connected to the wire receiving clip '50. The circuit between thev terminal screws 62 is as follows: plate'47, contact 60, contact 61, blade conductor 49,'plate 50, magnet coil end 67b magnet coil end 67a, terminal plate 52. I

A cover 68 fits about the portion 29b of the motor base 29 and is held thereon by a screw 69 extending through an aperture in the cover and into a tapped hole in the core 66. v

A horn mounting bracket '70 is secured to the flanges 25 and 28 by screws diaphragm 32 between these flanges.

It will be noticed that the armature head 35 is substantially greater in diameter than the core the base portion 29a in closely spaced relation to the edge of the base portion, so that a portion of the armature" head 35 substantially,

interrupts the direct line between the nearest parts of the core 66 and the pole piece 29a. Thus, though there may be some fringing out of the lines cram; between the core and pole piece, they will all pass over by way of the head 35. In so doing,

. the annular gap,

end 670; of which is connected to the 71 used to clamp the 66 and that it is movable within the aperture43 and the armature flange 36. The combined area greater than the area of these two gaps is much I or that gap between the' head of the axial gap,

35 and the core 6B. Therefore theflux density across the axial gap between the head 35.and the core 66 is much two gaps.

greater than across the other, The magnetic pullacross the cylindrical gap between the part 29aand the head 35 is at right angles to the movement of the head 35 and hence does not increase as the head 35 moves I toward the core 66 nor does it contribute anything to the pull upon the diaphragm. Apart only of the total flux inthe circuit is directed across the annular gap between the part 29a and the armature flange 36, but this is available-due to the,

reduced width of the annular gap to materially aid the magnetic pull upon the armature andrbee 1 comes most effective near the end of the stroke when the flange 36 approaches the part 2911, to increase the blow given by the armature to the core that causes the resonate good ringing tone. It will be observed,..too, that the axial gap is less inwidth than is the widthof can engage the part 2921.. Due tothe introduction d s to p o u a so that the armature head a1: ways strikes the 'core member before the 'flange'3fi' of the cylindrical gap that is of narrow extent and of considerable relative area, and across,

which part of the flux betweenthe' armature and part 29;; is directed, the flux. crossingthe wider annular gap of relatively great area will be-im effectiveto tilt the diaphragm outof its lineo f 2 proper movement. There are a number o'f elementsc'ontributingto this result; one of which is thatthere is less total flux crossing the ,'annular I 40 gap; another is that there is a small percentageof decrease in width of the gap for the-same angle of tilt of the armature flange; and still anotherf' moment arm throughp nular gap can operate v 1 that there is a short which the flux across the a to tilt the diaphragm.

There-fore, if the'flange 36-is slightly closer to the part 29a. at one'point than at a pointdiametrically Opposite, itis clear that the tendency to pullth'e diaphragm in a direction obliq'ue to-its axis w n bevery slight. This tendency will be overbalanced'by the tendency of the core ma tract the head in a direction 'at right angles to" the plane of vthe diaphragm, particularly sin ce f the head- 35 and the core 7 the axial gap between 66 is shortest at the ax ries the total flux, while i H cylindrical gap each carry only a portion of the total flux. As a result,

diaphragm only in a direction at righta nglesto it's plane, the diaphragm is caused to vibrate in a natural manner and to produce sound vibrations pleasing to the ear. 7 V froi'n its center'in a d ect'io'n' oblique to the normal movement of its center, it would setup vibrations producing a disagreeable noise.

l/Vh'i'le the form of embodiment of the present,

1501 these partsand car the annular, gap and the.

If the diaphragmwere pulled 1 ,7

H the pull upon the diaphragm is substantially always at rig-ht angles to the plane ofthe diaphragm. By pulling on the 3- atedby the magnet motor, said base being .ap'er tured coaxially with the core of saidilmagnet,

said armature having a main'headportion protruding through the said base in close juxtaposition to the magnet core and having a peripheral portion overlying a portion of the base adjacent said aperture, the air gaps between the'magnet core, and armature head and between the base and armature flange being so evaluated :as to shunt the major portion of the magnetic flux through the head of said armature duringactuating of the magnet motor. g 1

2. In a sound signal ,havinga vibratory motor including a magnet andfcore the combination comprising, a base apertured coaxial'of the core,

of said magnet and providing a polefpiece, and a flanged armature having a head portion disposed within and substantially filling said aperture, said armature having a flange overlying a portion of the base about said aperture, the air gap between the-base and armature head portion being'substantially constant such as to maintain substantially equal flux phenomena through that path during energization of, said, magnet motor, said apertured base'and flanged armature providing means for shunting the magnetic flux in the return path through the head of said armature and distributing it over an air gap of considerable area; l

3. In a sound-signal having a 'magnet motor, a vibratile diaphragm, and an armature mechanically tied to the diaphragm for operating the same, the combination comprising, afield member overlying said motor and apertured coaxially' of the core, said armature having a cylindrical head telescopically and centrally disposed in said aperture, the field member and armature head providing a tubular air gap of relatively small spacing, a flange secured to the armature head and extending over the body of the field member but spaced therefrom to provide an annular air gap of greater spacing than the tubular gap, the relation of the air gaps being such as to shunt the greater portion of the magnetic flux between the field member and the armature across the tubular gap. z

4. In a sound signal, the combination comprising, a linearly movable armature having a substantially cylindrical head portion, said head portion having an arcuate end surface; an armature disc adjacent the head portion and concentric therewith; a magnet motor having a core and yoke providing flux paths for the motor magnet flux, said core having a surface adjacent the arcuate surface of the said head portion and substantially concentric therewith, said yoke having a substantially cylindrical opening within which said head portion is mounted and moves axially of the opening, said yoke having a surface adjacent said disc and spaced therefrom, said head portion and disc and the spaces between said yoke and head portion and yoke and disc being so proportioned that the major portion of the magnet motor flux in the return path crosses the space between the head portion and yoke to thereby diminish the magnetic pull on the armature head portionacross the space between the yoke and armature disk. 7

5. In a sound signal of the vibratory type wherein a diaphragm forms the sole support for a movable armature, and in which a magnet motor is effective upon the armature to produce oscillation of the diaphragm, means for minimizing cocking of the diaphragm, said means including, an armature extension having a plane flange, abase plate fixedly supporting the motor and diaphragm, and apertured to receive the armature extension in closely spaced relation, said armatureflange being of greater'diameter than the aperture of the base plate to overlap a portion thereof; and means associating the base plate and armaturemassembly so that a greater flux density will obtain across the gap between the armature extension and base plate than across the gapv between the armature flange and base plate. "6. In a sound signal having a magnet motor providing a core, a vibratile diaphragm, and an armature carried by and spaced from the diaphragm, the combination comprising, a substan-' tially circular pole piece surrounding the armature in closely spaced relation and cooperating with the "armature to complete a substantially continuous path of magnetic material for the motor flux path,'a radiallyextending flange secured to the armature and greater in diameter than the pole piece to lay in spaced relation overan annular portion of the pole piece; the spacing of the pole piece and armature forming a cylindrical gap, and the spacing of the pole piece and flange forming a plane annular gap adjacent to and at right angles to the cylindrical-gap, and the'relation of the'twosaid. gaps beingssuchthat the cylindrical gap will be substantially of constant and of relatively dense magnetic flux, while the annular gap will be of variable and of relatively less dense magnetic flux, the flux across theannular gapincreasing near one extreme of the providinga core, a vibratile diaphragmyand an' armature carried by the diapmagm andactuatable by the motor to strike the core, the comma. tion ccmprising means causing all of the magnetic flux to pass between the core and armature, means for completing a substantially continuous path of magnetic material for the return flux, and means for distributing the return flux over a plurality of gaps so that there will be little tendency to actuate the diaphragm in a direction other than normal to the plane of the diaphragm, said distributing means comprising a pole piece included in the return flux path closely disposed and equally spaced about the armature to form a cylindrical gap, and'a flange on the armature overlapping the pole piece and spaced therefrom to provide an annular gap adjacent and at right angles to the cylindrical gap, the cylindrical gap carrying a larger portion of the return flux between the armature and pole piece, whereby the annular gap may be reduced in width to provide an added pull to the diaphragm during actuation without effecting the proper movement of the armature in striking the core.

8. In a sound signal of the vibrator type the combination comprising, a mounting plate apertured to provide a pole piece, a magnet motor including a core member attached to the pole piece to form a magnetic path, a diaphragm supported by the plate, a flanged armature carried by the diaphragm and having a main body portion disposed within the plate aperture to provide a tubular air gap of substantially constant magnitude, while the flange projects over the adjacent portion of the plate to provide an annular air gap of varying magnitude, the armature body being immersed in the flux path between the core member and pole piece, the relation of said air gaps being such as to reduce the reluctance of tured to provide a pole piece, a magnet motor in-' cluding a core member. attached to the pole piece to form part of a magnetic path, said core member being disposed on one side of said pole piece and substantially concentric to the aperture there in; a diaphragm, an armature supported by the diaphragm and having a portion centered within the aperture of said pole piece forming an axial gap with the core and a tubular gap of close spacing with the aperture wal1,and a flanged portion extending over the-pole piece forming an annular gap of greater spacing than the'tubul'ar gap, means to concentrate the pulling force of said magnet motor at the axis of said core member, the relation of-the tubular and the annular gaps being such as to distribute. thegreater portion of the return flux across the tubular gap so that only a-lesser portion of the return flux will be.

effective across the annular gap and in aiding relation to the pull upon the armature.

10.. In a sound signal of the vibrator type the combination comprising, a mounting plate apertured to provide a pole piece, a magnet motor ineluding a core member attached to the pole piece tofform a magnetic path, a diaphragm supported by the plate,ban armature carried by the dia- I phragm to be immersed in the flux path between the core-member and pole piece, and having a head portion centered in and closely surrounded by the plate aperture to form a tubular air gap,

and also havinga flanged portion overlapping an annular'p'ortion of the mounting platefitovfdfm a plane-like air gap substantially at right "angles to and adjacent to the tubular air gap, andmeans to confine the magnetic flux between the core and armature .at the axis of said core, the relation of said head and flange with the pole piece provid ing means to divert the return path ofsaid Inagnetic flux across a plurality-of gaps, so that only.

is ineffective to assist V a portion of the return flux the magnetic puil-uponth'e armature. V

11. m a sound. signal of the vibrator type the combination comprising, a mounting plate aperitured to provide a pole piece, a magnet motor-in cluding'a core member attached to the pole piece to form a part of a magnetic path, an armature having a head portion insertablethroughsaid pole piece tolie in closely spaced relation and concentricv with theiwall of said aperture and a flange portion joining the head portion to'extend" radially over thepole piece about the aperture;- so that the pole piece and armature portions will complete a substantially continuous path of mag netic material for the mag'neticcircuit andprovide two angularly associated airgaps betweenthe armature and pole'pie'caa'diaphragm sup- 1 porting the armature 25",; and maintaining it substantially coaxial ofthe pole piece aperture, meansto concentrate the magnetic flux between thec ore member and armature iatthe axis thereof, the relation of the pole piece and armature portions being such as to direct the return-flux across the angularly associated and adjacent air gaps, so-that:

the gap between the armature head and polepi'ece will have the greater flux density and be of sub-' stantially constant value, and so that the gap between the pole piece andflange portionswillbe oflesser flux density due to the relative-cross section and areas of both gaps. 1 7

ROBERT M. oai'ronninnn f 

